This is how I feel when I send hordes against my players: that said, sometimes it is necessary. I hate long fights I know that I'm going to have to hunker down for a long battle knowing this is going to take 2 hours of the 4 that we have to play once/week. My players are all very optimized and very effective at bringing down one opponent. My tactic has been to throw more opponents and it really does work. Try it even though it will mean longer time at the table.

Also, I agree with the incorporeal opponent, slimes/oozes, and something that it hurts to touch like spiked armor or a thorny body, etc.

This is how I feel when I send hordes against my players: that said, sometimes it is necessary. I hate long fights I know that I'm going to have to hunker down for a long battle knowing this is going to take 2 hours of the 4 that we have to play once/week. My players are all very optimized and very effective at bringing down one opponent. My tactic has been to throw more opponents and it really does work. Try it even though it will mean longer time at the table.

Also, I agree with the incorporeal opponent, slimes/oozes, and something that it hurts to touch like spiked armor or a thorny body, etc.

Yeah, the horde isn't fun to manage, but it's pretty much the only way to challenge a group that's being protected by giant crystals with obscene grapple scores. What's more, since the horde is made up of lower-level enemies, it's easier for the dead weight fighters in the party to contribute.

You can mitigate the bookkeeping if you use classes or monsters that have a short list of abilities Maybe have your brutes be Ogre Zombies or Trolls instead of Fighters, and use "spellcasters" with relatively few options like Shadowcasters or Warlocks.

I don't see monsters that deal damage in grapples being all that effective, because Astral Constructs are totally expendable. Once the encounter is over, it doesn't matter how much damage it's taken, it's going to get replaced soon after.

I am DMing a game with a Psion, a Cleric, a Wizard, and a Ranger/Rogue, and all of them can hold their own in a wide variety of encounters. the module that I am using calls for lots of single-monster fights, so I have to do any of the following: beef up the monsters; add more monsters; surprise the PCs; replace the monsters; give them more encounters in a day; play the monsters smart.

there are level-appropriate monsters that bring tough choices for grapplers - Fire elementals, for example. If you grapple one of these guys, they stand a chance of reversing it and burning the astral construct. And elementals have DR. Throw in a spell caster who can put up a Wall of Fire around the AC and the elemental.

Surprise the psion with a grapple to open the fight. "You enter the throne room, and from the shadows in the ceiling, a giant spider lands on you!" If the spider wins initiative, it spins a web around the psion. Meanwhile, all sorts of other vermin swarm the rest of the party. Lots of low-level mooks. You might have ten monstrous spiders, but DMing is easy since they all have the same stats. If they're scattered all around, a fireball won't take them out either, and if the party huddles together they're easy pickings for webs and AOEs from the bad guys.

Put dangerous terrain in a fight. "Oh, by the way, make a reflex save. The spot on the floor you are on, it just caved in." "Everyone within 30 feet of the monolith, make a fort save or take 1d8+10 from its Mass Inflict Light Wounds SLA. And the skeletons are all healed that much."

Monsters know all the strengths and weaknesses of their lairs. Smart enemies can spring traps, send their number in waves, snipe, ambush, surprise, etc.

If the psion metagames, throw in a curveball. Rust Monster is to metal weapons as X monster is to astral constructs. Oh look, here's a few of X monster that will destroy the construct. This is admittedly targeting the AC, but if there are recurring enemies, they'd be studying the party as much as the party studies the enemies, right? The first time I threw a Crystal Golem (aka psion-killer) AND a sorcerer at the PCs, they got real scared. They were around level 14 when I threw the CG and a level 11 sorcerer at them. The sorcerer kept casting Stinking Cloud, and the CG and the AC had to duke it out in the cloud. Once the PCs got their wits back, they got to gang up on the sorcerer. Meanwhile the 14th level psion couldn't use Energy Missile, Mind Thrust, or anything else all due to a 3rd level spell.

As PCs get to higher levels, they amass wealth and magic items. Any wizard or cleric worth their appellation will also scribe scrolls, brew potions, have wands and staves, etc, on top of appropriate spell selection. You can really throw anything you want to at higher-level parties.

there are level-appropriate monsters that bring tough choices for grapplers - Fire elementals, for example. If you grapple one of these guys, they stand a chance of reversing it and burning the astral construct. And elementals have DR. Throw in a spell caster who can put up a Wall of Fire around the AC and the elemental.

Whether the Fire Elemental is grappling the AC or the AC is grappling the Fire Elemental, the AC is serving it's purpose, and any damage dealt to it in any case is entirely pointless unless it gets one-shotted (at which point it's only mostly pointless).

Surprise the psion with a grapple to open the fight. "You enter the throne room, and from the shadows in the ceiling, a giant spider lands on you!" If the spider wins initiative, it spins a web around the psion. Meanwhile, all sorts of other vermin swarm the rest of the party. Lots of low-level mooks. You might have ten monstrous spiders, but DMing is easy since they all have the same stats. If they're scattered all around, a fireball won't take them out either, and if the party huddles together they're easy pickings for webs and AOEs from the bad guys.

Psions don't care about being grappled, they'll Psi D.Door away and then summon the necessary number of ACs.